If the only notion of a real physical threat is two dudes punching each other. Lex Luthor is supposed to be a threat because he comes at Superman in two ways that his powers can't beat: Lex's intellect and Lex's resources. Having Kryptonite ruins any chance of seeing Lex's brains on display at all. Getting lucky and finding a deus ex machina rock doesn't prove your intelligence at all.

Seriously guys, Kryptonite is the least necessary aspect of the Superman mythos. Not having it forces the writers to write smarter. Not having it just makes the story better.

I like your way of thinking kryptonite stories always seem poor in comparison to non Kryptonite stories to me.